The present invention relates to pneumatic tires for wheels of any type, which are provided with a radial carcass, that is with a carcass formed by one or more plies the threads (fine cords) of which lie in planes passing through the axis of rotation of the tire, or form small angles with said planes.
Tires with radial plies have notable advantages compared with those provided with a carcass having cross plies.
In the latter the direction of the threads is alternately crossed in passing from one ply to that immediately following.
It is however known that radial tires have, in correspondence with their walls, an excessively high flexibility which on one hand has the advantage of a considerable degree of comfort, while on the other hand can lead, under working conditions, to excessive bending of the walls and therefore to tangential movements.
This can in consequence cause premature wearing out of the tire in those areas of the walls, connected with the bead, which are in contact with the mounting rim.
In order to eliminate, or at least to reduce, this disadvantage, different solutions have been considered which are essentially based on devices adapted to increase the rigidity of the area of the walls connected to the bead.
Therefore supplementary bands of plies have been introduced, crossing or not crossing each other and the radial plies of the carcass, and this to an extent dependent upon the degree of required rigidity.
Particularly effective seems to be the solution which entails the introduction of supplementary plies with threads parallel to or inclined to those of the carcass, made with materials of relatively low flexibility.
It will suffice to mention for this purpose the combination of a radial carcass of textile threads and of reinforcements, crossed with it, formed by metal filaments.
An example of such a solution is disclosed in the Italian Patent Specification No. 942,682.
The preceding solutions are, however, not without disadvantages taking into account the following considerations.
The added reinforcement materials are formed by fabrics different from those of the carcass, which have to be, therefore, prepared separately, cut to size, gathered and positioned separately during the manufacture of the tire. This causes complications in the process, with loss of time and high costs.
Furthermore, as the elements are detached the dangers of positioning and of faulty anchorage have to be considered. These elements can shift during molding and vulcanization of the tire and get into undesirable positions or into positions not completely suitable in view of the results one wishes to attain.
Finally said fabrics, of a different nature than those of the carcass, form heterogeneous elements the efficiency of which is difficult to foresee, especially if one takes into account the fact that one requires a gradual stiffening beginning with the most flexible zone of the wall of the tire, to the zone of the bead which is in itself relatively rigid.
Notwithstanding the said disadvantages very rigid fabrics are usually used as reinforcement elements for the walls of the tire.
In other words there is a tendency to use a minimum number of reinforcement elements in order to reduce the possibility of incorrect positionings and to simplify the process of preparation of the tires.